Calculators/Concrete

Concrete Footing Calculator

Estimate concrete volume for rectangular footings used under walls, small structures, posts, and foundations.

Last reviewed: June 2026

ft

Enter length in feet. If continuous, enter total length.

in
in
%

Results update automatically as you enter measurements.

Your Material List

For this project, buy or order approximately

Use these quantities as a shopping list, supplier note, quote check, or quick jobsite material estimate.

Bags Required
19Bags
Volume per Footing
10ft^3
Total Volume
11ft^3
Total Volume
0.407yd^3
Notice: Footing dimensions (width and depth) are often strictly controlled by local building codes, soil bearing capacity, structural loads, and regional frost depth lines. Always consult local codes or a structural engineer before pouring.
Note: Bag yields vary by manufacturer. Always verify the yield on the bag packaging.
Estimate note: Actual needs vary due to compaction, grading, cuts, bag yield, and supplier differences. Confirm requirements before purchasing.

Formula and Assumptions

Formula used

Footing volume = length × width × depth, with inches converted to feet first. Total volume = one footing volume × number of footings. The calculator applies your waste percentage, then divides by the selected bag yield to estimate total bags.

Unit conversions

Inches are converted to feet before volume is calculated. Cubic feet are converted to cubic yards by dividing by 27. Bag counts are rounded up because stores do not sell partial bags.

Waste factor explanation

Waste factor helps account for uneven surfaces, cuts, spills, compaction, settling, and measurement differences. The right buffer depends on your project and material.

Material Assumptions and Disclaimer

Bag yield or density assumptions

  • The footings are perfect rectangular prisms.
  • Standard average concrete bag yields are used.

Estimate disclaimer

These tools are useful for DIY planning and quick jobsite estimates, but the results are still estimates. Verify quantities for structural work, code requirements, supplier material specs, product labels, or professional requirements before purchasing or quoting a job.

When to be careful

  • Footing dimensions are often strictly controlled by local building codes based on frost lines and structural loads.
  • For structural projects, always consult a professional engineer or architect.

Example Calculation

Pouring 2 footings, each 8 feet long, 16 inches wide, and 12 inches deep. Using 80-lb bags with 10% waste:

  1. Convert 16 inches to feet: 16 ÷ 12 ≈ 1.33 ft
  2. Convert 12 inches to feet: 12 ÷ 12 = 1 ft
  3. Volume for one footing: 8 × 1.33 × 1 ≈ 10.66 ft^3
  4. Multiply by 2 footings: 10.66 × 2 = 21.32 ft^3
  5. Add 10% waste: 21.32 × 1.10 = 23.45 ft^3
  6. Divide by 80-lb yield: 23.45 ÷ 0.60 = 39.08 bags
  7. Round up to nearest bag: 40 bags.

You need 40 80-lb bags for the two footings.

Frequently Asked Questions

How deep should a concrete footing be?

Footing depth depends on local building codes and the frostline. In colder climates, footings must extend below the frost line (which can be 48 inches or deeper) to prevent freezing and thawing from lifting the structure.

How wide should a footing be?

As a general rule, a footing should be twice as wide as the wall or structure it supports. So, an 8-inch block wall would generally have a 16-inch wide footing.

Do I need rebar in my footings?

Yes, almost all structural footings require steel rebar to provide tensile strength to the concrete and help prevent cracking. The size and spacing of rebar will be determined by your project plans or local codes.

Can I pour footings directly in a dirt trench?

Often yes, a technique known as "earth-formed footings" is common if the soil is firm and cohesive enough to act as a form. However, if the soil is loose or sandy, you may need to build wooden forms.

How many bags of concrete can I comfortably mix by hand?

Mixing concrete by hand is physically demanding work. Most DIYers find that anything over 30 to 45 bags (around 1 cubic yard) is better suited for a concrete delivery truck or a portable power mixer.

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